1. The Field of the Invention
The present invention relates generally to removal of organic-based wastes from sludge ponds. More specifically, the present invention relates to devices for removing sludge from sludge ponds, which sludge may then be directly applied to agricultural land, or used to produce organic fertilizers by processing the organic-based sludge.
2. The Relevant Technology
Feedlots, animal barns, municipal sewage, and farms that keep large numbers of animals are sources of enormous quantities of organic waste. The expression “organic waste source” will hereinafter refer to any of these sources of organic waste or to any source that similarly produces organic waste, although perhaps in different quantities or by different activities.
The disposal of untreated organic waste causes serious pollution problems which include those due to the waste's high content of chemically oxidizable components and biochemically decomposable components. When these pollutants reach bodies of water, either because they leach from disposal sites or as a consequence of being directly released or transported into water bodies, they deoxygenate the receiving waters and impair the receiving waters' capability to support aquatic life.
Acridity and high pathogen content present additional problems of untreated waste disposal. Acrid gases released into the atmosphere are not only unpleasant but they can also contribute to acid deposition, global greenhouse effects, and ozone depletion.
Organic waste that is left to run off into adjacent bodies of water or onto adjacent land is generally high in nitrogen and phosphorous, and has been linked to various dangerous toxic microorganisms.
In hog and cattle raising operations, water is typically used to flush waste out of barns and into storage facilities, thus producing a slurry that can be up to 97% liquid. The flushed waste is typically stored in earthen sludge ponds, sometimes referred to as lagoons. Most of the solids (including as much as 90% of the phosphates) settle as part of the sludge layer at the bottom of the pond. A large percentage of the nitrogen and potassium nutrients are entrained as soluble salts within the sludge layer. A relatively small percentage of these nutrients remains dissolved in the dilute layer, while some of the nitrogen also volatilizes into the atmosphere.
Sludge ponds have a limited useful life, and eventually must be cleaned out by removing the liquids along with the sludge layer. In addition, because of the high costs and environmental disadvantages of operating large sludge ponds, there has recently been increased pressure to use alternative treatment techniques that either require smaller lagoons or no lagoons at all.
In an attempt to recoup some of the cost of cleaning out such lagoons, methods and apparatus have been developed to retrieve some nutrient value of the organic waste, which can be used as a fertilizer. One method for retrieving some nutrient value of the organic waste in sludge ponds involves pumping the liquid out while agitating the sludge layer at pumping time to capture the nutrients that otherwise would remain behind in the lower settled layers. This slurry is then applied to agricultural land, often turning or knifing it into the soil. Because the sludge layer is mixed with the liquid dilute layer, the retrieved mixture has a relatively low nutrient concentration.
Another method involves dredging the sludge layer, which is then air-dried and then applied to agricultural land. Dredges operate at relatively high flow rates (e.g., 700–800 gpm). With current dredges and at these rates, there is a great deal of turbulence, vortexing, and mixing created between the sludge layer and the dilute layer, which results in column mixing of the layers. Mixing of these layers lowers the concentration of nutrients within the retrieved mixture.
In addition, each of these methods and apparatus involve relatively high equipment and operational costs. The cost of equipment and operation is often exacerbated because in many cases the animal raising operation is closing because of financial difficulties.
It would be an improvement in the art to provide a device and method that could be used to efficiently and inexpensively remove a high nutrient sludge product from sludge ponds, which sludge could then be either directly applied to agricultural land or used to produce a certifiable organic or other fertilizer.